For those that ride down South away from the PanAm countries I would strongly suggest getting the license, there are actually two that you can get, IIRC one works for Brazil where the other doesn't. Crossing out of Venezuela into Brazil at Santa Elena I was asked for my International Drivers license on the Brazil side along with my state issued drivers license that is required along with the international permit and damn it I didn't have just 10 or so days left on my OK drivers license and they weren't going to give me more time in country than my license was valid for Glad I only needed to go down to Manaus and drop off some tires or I would have been in a bit of a bind.

It's cheap to get them and you can get a little creative with them and make them last for more than a year using a rubber eraser

In Latin America they love their paper work so why not throw two more international drivers licenses at them Brazil was the only place so far that has ever asked for one btw Pan American side ought to be all clear.